1. Field of the Invention
The present invention relates to a magnetic type encoder, and particularly to a magnetic type encoder in which a mounting construction of a cap is improved.
2. Prior Art
FIG. 3 is an explanatory view showing a conventional magnetic type encoder. In this figure, a magnetic drum 1 has its surface magnetized in multi-polarity. The magnetic drum 1 is fixedly mounted on a rotational shaft 3 of a motor 2. The rotational shaft 3 is rotatably supported on a bearing portion 5 of a motor base 4, and the motor base 4 is fitted in and secured to a motor housing 6 for covering a rotor 12 of the motor 2. An encoder base 7 is fixed by screw B onto the motor base 4, and a sensor not shown is mounted on the encoder base 7. A mounting member 9 is bent around the sensor. A cap 10 covers the magnetic drum 1, the sensor and the like, and is fastened at its lower end to the mounting member 9 by screw 11.
In the above-described prior art, since the cap 10 is fixed by screw 8 to the encoder base 7, when an external force is applied to the cap 10, the encoder base 7 is also deviated from the rotational shaft 3. The sensor is mounted on the encoder base 7 in a spaced relation (gap) from the magnetic drum 1. However, when the gap is outside a predetermined range due to the aforementioned deviation, it is not possible to obtain an effective detection signal by the sensor.